56 NEW YORK STATE MUSEUM 
stone. As is the case with the Siluric, the rock formations are 
piled one upon another like great sheets and all show a gentle 
southward dip (see figures 3 and 5). Beginning at the bottom, the 
Helderberg limestone was succeeded in regular order by the Oris- 
kany sandstone, Onondaga limestone, Marcellus and Hamilton 
Fic. 18 Generalized map of North America in the Devonic period, show- 
ing the relations of land and water. Horizontal lined areas=land; blank 
areas — water. Only the northern and extreme southeastern portions of the 
New York State atea were land. The western shore of Appalachia was far- 
ther west than during the Ordovicic, due to the addition of the Taconic 
mountain area 
shales, all of which were deposited over the whole Devonic basin 
in New York. Above these come the Tully limestone and Genesee 
shale which extend from east-central to western New York. Still 
higher, and forming the summit of the Devonic, are the Portage 
shales and sandstones and the Chemung (or Catskill) sandstones 
